S4.13.8 For the adult
Speakers and microphones
A loudspeaker makes sound from a wire. A microphone makes a signal in a wire from sound. What is inside them, and how do they work?
What this chapter teaches
A loudspeaker has a coil in the field of a magnet. An alternating current makes a force on the coil, by the motor effect, which moves the cone in and out and makes sound. The frequency is the pitch and the size of the current is the loudness. A microphone is the same idea reversed: sound moves a coil in a field and induces a voltage.
Three questions to ask
There is no one right wording. Listen for the idea.
- How does a current in a loudspeaker become sound?
- Why does a steady current in a speaker not make a sound?
- What are the magnet and the coil doing in a microphone?
After the chapter, the learner can
- Explain how a loudspeaker turns current into sound
- Explain how a microphone turns sound into current
- Find the magnet and coil inside an old broken speaker
What they copy into their notebook
Loudspeaker: current in a coil in a field, force, cone moves, sound. Microphone: sound moves a coil in a field, voltage induced. Pitch is frequency. Loudness is the size of the current.